The present invention relates to a gear shift hydraulic apparatus for a vehicular automatic transmission in which an idle stop control is equipped. In particular, the invention relates to a gear shift hydraulic pressure apparatus applicable to a belt type continuously variable transmission (so-called, CVT).
A previously proposed shift hydraulic apparatus for a vehicular automatic transmission is described in a pre-publication of academic lecture meeting of an automotive vehicle technology society (No. 67-00,20052220, titled Hydraulic and Electronic Control System of CVT for Hybrid Vehicle). In this paper (pre-publication), a technique of an idle stop vehicle in which a belt type continuously variable transmission having only an engine driven pump is mounted. In the system of the vehicle, a wet clutch is used as a start clutch and during a re-start of the vehicle after the idle stop, an engagement torque of the start clutch is regulated by means of an electronic hydraulic actuator and a timing of a rise in a transmission torque of a forward clutch is delayed at an earlier timing than that of a rise in a transmission torque of the start clutch. An orifice is adjusted on the hydraulic pressure circuit so that an occurrence of a belt slip of the CVT caused by a drain hydraulic pressure reduction immediately after the engine is restarted is prevented.
On the other hand, a hydraulic circuit has previously been proposed as another previously proposed shift hydraulic apparatus for a belt type continuously variable transmission in which a normally available torque converter is used as the start clutch. In the latter previously proposed hydraulic circuit, a delivery outlet (drainage outlet) of an oil pump is communicated with a pressure regulator valve regulating the pressure of a line pressure via a first oil passage. In addition, pressure regulator valve is communicated with a clutch regulator valve via the first oil passage. A drainage pressure of the oil pump is regulated by means of pressure regulator valve and a pulley clamp pressure is supplied from the drainage of the oil pump via a second oil passage. A third oil passage is provided having a first orifice on the third oil passage. A clutch regulator valve regulates a relief pressure of the pressure regulator valve and the line pressure supplied via the first orifice from the third oil passage so as to regulate a forward clutch pressure. A pilot pressure regulated by means of a pilot valve supplies an original pressure of each lock-up solenoid and a select switching solenoid via a fourth oil passage. Operations of a select switch valve and a select control valve are controlled in accordance with each corresponding solenoid. That is to say, each of the above-described lock-up and select solenoids controls select switching valve and select control valve. During an engine restart, the hydraulic developed from oil pump supplies the pulley clamp pressure via the second oil passage and the hydraulic is supplied to the forward clutch via such a route as a fifth oil passage from the clutch regulator valve→a sixth oil passage branched from the fifth oil passage→the select control valve→a seventh oil passage from select control valve to the select switching valve→select switching valve→an eighth oil passage from the select switching valve to a manual valve→the manual valve→a ninth oil passage. In a case of the previously proposed hydraulic circuit described above, an input torque immediately after the start of the vehicle is uniquely determined according to an engine speed and characteristics that the torque converter naturally has (a torque capacity coefficient and a stall torque ratio). In addition, on a hydraulic circuit of the forward clutch, an oil pump draining pressure is communicated with the first orifice so that the rise in the forward clutch engagement (clutching) pressure is delayed at a later timing than that of the rise in the pulley clamp pressure. Thus, the belt slip of the CVT and a shock due to a surge pressure developed at a clutching time of the forward clutch are prevented from occurring.
However, in the latter previously proposed hydraulic apparatus, during the engine restart after the idle stop is ended, the input torque is automatically determined depending on how the rise in engine speed is carried out. Furthermore, the hydraulic supplied to forward clutch is the line pressure via first and second orifices. The second orifice is interposed in the oil passage from the manual valve to the forward clutch. Hence, the rise in the forward clutch engagement (clutching) pressure is remarkably or extremely delayed. Consequently, a large shock is developed during the clutching of the forward clutch.